Ambient Occlusion Solid Mode and Edit Mode
The closest thing that exists in 2.8x that I know of is the cavity setting, in the viewport shading settings.



The "Valley" setting is the closest thing to the old "Strength" setting from 2.79b that I can find. Here is a comparison of the 2.79 viewport with AO enabled and the 2.8 viewport with Cavity Type: World enabled.





Hope this helps!